Do not call setOption if mMhlController is null

[Root Cause]
The system crashes sometimes because we didn't check if mMhlController exists.

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.android.server.hdmi.HdmiMhlControllerStub.setOption(int, int)' on a null object reference

[Solution]
Check if mMhlController is null before calling setOption.

[Test Report]
AC off/on: PASS

Bug: 380905499
Flag: EXEMPT bugfix
Change-Id: Id21a35b8c9bb00e49a862ad2aca02ccbb3b0e9b9